1. Field of the Invention
The present invention relates to the field of nuclear medicine. Particularly, the present invention relates to the field of transmission scanning to provide nonuniform attenuation correction within a gamma camera system.
2. Background of the Invention
Non-uniform photon attenuation is an important factor that affects the quantitative accuracy of images collected using Single Photon Emission Computerized Tomography (SPECT) camera systems and can decrease the sensitivity of these systems for lesion detection. Nonuniform photon attenuation distorts images by interfering with and partially absorbing the radiation emitted from an organ containing a radio-pharmaceutical. Photon attenuation within SPECT systems tends to degrade images by also introducing image artifacts and other distortions that can result in false positive detection or the undetection of lesions. The effects of photon attenuation are especially complex in cardiac studies as a result of nonuniform attenuation attributed to the thorax.
In transmission scanning, the source of radiation is directed toward the associated scintillation detector through the object of interest or patient. If the radiation field is significantly larger than the patient, the radiation source is allowed to directly radiate the detector, causing a high count rate in the scintillation detector. Those parts of the detector that become directly radiated are called unobstructed portions of the detector. It is not advantageous to allow large unobstructed detector areas because the resultant increase in count rate can lead to image degradation and in some cases the event detection electronics and processes can become overloaded (e.g., due to pulse pile-up) and temporarily terminate operation. These high count rates tend to reduce the imaging performance of the imaging system by loading down the signal detection and processing circuitry of the gamma camera.
Transmission computed tomography (TCT) can be used as a method for generating a nonuniform attenuation correction distribution. The transmission image data is gathered using a known source (e.g., line, sheet, or flood) of radiation. If performed separately from the SPECT emission study, the collection of the transmission data requires additional data acquisition time and the collection of the transmission and emission data is susceptible to misregistration effects due to patient (e.g., "object") movement between the data gathering sessions.
However, whether the transmission data is collected simultaneously with the collection of the emission data or not, the patient is generally exposed to additional radiation in order to collect the transmission data. Depending on the size and shape of the patient, different amounts of transmission radiation are required in order to collect the minimum required amounts of transmission data. Systems overexpose the patient with transmission radiation in order to obtain the minimum required amount without regard to the shape or size of the patient. What is needed is a system that can effectively minimize the exposure period of the patient to radiation utilized in collection of the transmission data by considering the particular size and shape contributions of the patient. The present invention offers such advantageous solutions.
Accordingly, it is an object of the present invention to provide improvements within gamma camera systems utilizing nonuniform attenuation correction techniques for improved image quality generation. It is an object of the present invention to determine the minimum exposure time required for the most attenuating portion of a scanned object during a transmission study. It is an object of the present invention to provide the above while considering the size and shape contributions of a particular patient. It is another object of the present invention to provide a reduced radiation exposure period for generation of transmission data used in creating a nonuniform attenuation correction distribution. These and other objects of the present invention not specifically mentioned above will become clear upon discussions of the present invention herein.